Efficiency improvements in photovoltaic solar cells are of vital importance to the success of solar cell technology. Plasmonic effects from metallic nanoparticles are capable of improving solar cell performance. If the nanoparticles are integrated into photovoltaic devices with a relatively low surface coverage (usually below 30%), light trapping from plasmonic resonances of the nanoparticles can increase the solar cell absorption, and can thereby enhance the efficiency of conversion of sunlight to electrical energy in the solar cell.
However, plasmonic nanostructures can suffer from destructive absorption, so that the efficiency of plasmonic solar cells is limited, as described in Reference (1). For example, it is a great challenge to increase the efficiency of textured crystalline silicon solar cells to above 19% using conventional plasmonic processes, as described in Reference (2). The destructive absorption of plasmonic nanostructures that reduces solar cell performance is caused by two mechanisms: the Fano effect; and parasitic absorption above the plasmonic resonance that does not contribute to photocurrent.
The Fano effect refers to a destructive interference between the trapped and untrapped light that occurs below the resonance, as described in Reference (3). Among plasmonic materials, aluminium (Al) has a plasmon resonance in the ultraviolet range, where the intensity of solar irradiance is negligible: accordingly, Al-enhanced photovoltaic devices may be used to avoid the Fano effect, and thus improve solar cell efficiency compared to solar cells with silver (Ag) and gold (Au) nanoparticles. However, synthesizing Al nanoparticles and controlling their coverage to be sufficiently low has proven difficult: e.g., Al nanostructures can be too active to be produced by wet-chemical methods at ambient temperature. Although Al nanostructures can be obtained by evaporation of a metal thin film onto a solar cell surface followed by an annealing process, it is difficult to achieve a surface coverage below 30%, as described in Reference (4), and a high coverage of the nanoparticles blocks a significant amount of light, and thereby reduces the solar cell absorption.
The parasitic absorption above the plasmonic resonance that does not contribute to photocurrent is described in Reference (5). This negative effect may be compensated using light trapping materials or structures integrated into the solar cells; however, optical structures deposited on solar cells, e.g., pyramid textures and antireflection coatings, can be complicated or expensive to fabricate.
It is desired to address or ameliorate one or more disadvantages or limitations associated with the prior art, or to at least provide a useful alternative.